From the Institute course on fasting: The Definition of fasting
https://youtu.be/CYlXGngKMlI?feature=shared
If you want the truth, then seek the old books
https://youtu.be/CYlXGngKMlI?feature=shared
https://youtu.be/sfmVG40KePo?feature=shared
https://youtu.be/E3Z488shd4M?feature=shared